1. Field of the Invention
This invention relates to a process of manufacturing injection moldings in an injection mold which comprises at least two mold sectons, enclosing a molding cavity adapted to be supplied with the molding material through at least one entrance opening formed in one of said mold sections, in which process the mold is maintained at a solidification temperature for the molding material injected in a liquid state at a different temperature and consisting particularly of plastic material or another hot-settable or hot-vulcanizable material.
This invention relates also to an injection mold for a manufacturing injection moldings by said process, which mold comprises at least two mold sections adapted to be temperature-controlled at least in part and enclosing a molding cavity adapted to be supplied with molding material through at least one entrance opening formed in one of said mold sections.
2. Description of the Prior Art
If there is a relatively large temperature difference between the molding material and the mold in the known manufacture of injection moldings, the entrance opening merging into the cavity is provided at the end of a feed passage formed in the mold. Molding material is supplied to the cavity from an injecting machine or from a mixer. Injecting machines are preferably used in the processing of materials which solidify as they are cooled, such as thermoplastics, e.g., PVC, and injection machines or mixers are used for processing hot-settable or hot-vulcanizable materials, which are supplied as liquid silicones or rubber. Relatively small injection moldings can be made in a multi-cavity mold, which has a spider gate consisting of runners extending radially from a central sprue. The feed passages and the spider gate are at the same temperature as the mold so that the injected material solidifies in said passages and after the molding operation the injection moldings must be severed from the ends of the sprues or spiders. This operation is difficult and involves damage to the surface of the molding and a formation of flashes at the junction to the sprue so that the injection moldings may not be satisfactory for applications involving high requirements, e.g., in electric or electronic products. The material of the sprues or spiders is lost although in the manufacture of small injection moldings said material may have a larger mass than said moldings. Said material cannot be recycled if it consists of fully vulcanized rubber or of solidified two-component material. As it is not possible in numerous cases exactly to control the quantity of each batch which is supplied, excess molding material is used most cases in. This fact and other factors, such as a supply of material in surges or the provision of overflow pockets for receiving excess material in injection molds for molding rubber will result in a formation of flashes on the injection moldings, e.g., at the parting lines of the mold so that the molding must subsequently be machined. In the filling of complicated molds or multi-cavity molds, difficulties may arise during the filling of the mold owing to the air which is enclosed in the hollow space consisting of the cavity and feed passages. For this reason the temperature difference between the injected material and the mold can be controlled only with difficulty. For instance, in the processing of two-component liquid silicones the temperature of the molding material in the feed region should not exceed 20.degree. to 40.degree. C. but the cavity may have to be heated to, e.g., 240.degree. C. in order to effect a solidification and to ensure that the injection molding has the desired final properties.
Owing to the difficulties outlined hereinbefore, numerous components are made by other processes and in different apparatus. Insulating silicone or rubber bushings for electronic equipment and computers have previously been made from mats by pressing in a multi-stage process. In said case a subsequent machining is also required to sever each bushing from the mat and to expose the openings of the bushings. Contact mats providing a carrying structure for the key fields of computers, pushbutton telephones and typewriters are also made from mats in a process in which individual contacts are made and placed on a baseplate, whereafter the mat material is applied and a pressing or injection molding operation is subsequently performed. Contact mats are often made in a plurality of layers, each of which extends throughout the area of the mat and consists of a single material. That material is expensive. Such mats have only a very small inherent stiffness and can be handled only with difficulty. For this reason the contact mats are installed by hand. This operation must be carefully performed in order to prevent a deformation of the mats under tension.